1. Field of the Invention
The present invention relates to a security sensor device of a kind including a beam projecting unit, having a plurality of beam projectors, and a beam receiving unit having a plurality of beam receivers for receiving sensing waves such as an infrared beam, projected from the beam projectors towards the corresponding beam receivers so that the presence of a human body or the like can be detected when those sensing waves are simultaneously intercepted by the human body or the like. The present invention relates in particular to the adjustment of optical axis between each of the beam projectors and the respective beam receiver.
2. Description of the Prior Art
The security sensor device of the kind referred to above generally includes a beam projector for projecting a sensing wave such as an infrared beam and a beam receiver for receiving the optical detecting beam projected from the beam projector. An optical axis of the beam projector is aligned with that of the beam receiver. This security sensor device has a capability of defining an alert area or coverage ranging from a close range to a long range in terms of a linear distance so that the security sensor device can monitor the alert area as to the presence or absence of an intruder entering the alert area.
The adjustment of optical axis between the beam projector and the beam receiver is generally carried out during installation or maintenance servicing of the security sensor device in such a manner that the attendant worker looking through a sighting instrument manipulates an optical axis adjusting mechanism for moving the beam projector or the beam receiver in any of vertical and horizontal directions to perform a coarse adjustment of the optical axis. After this coarse adjustment of the optical axis, the attendant worker further manipulates the optical axis adjusting mechanism to perform a fine optical axis adjustment relying on a display indication of the level of light received by the beam receiver until the display indicates the maximum level of light received by the beam receiver. See, for example, the Japanese Laid-open Patent Publication No. 2002-279539.
It has, however, been found that the optical axis adjustment referred to above tends to become complicated, cumbersome and time-consuming particularly where a beam projecting unit makes use of upper and lower beam projectors and, similarly, a beam receiving unit makes use of corresponding upper and lower beam receivers. Specifically, where the beam projecting and receiving units are so arranged as to enable the upper and lower beam receivers to receive two infrared beams projected from the upper and lower beam projectors, respectively, so that an unauthorized entry of a human body into the alert area can be detected when those infrared beams are simultaneously intercepted by the human body, and if the alert area is defined a substantial distance away from the position of the beam projecting unit, the infrared beam projected from one of the upper and lower beam projectors tends to be received simultaneously by the upper and lower beam receivers as the projected infrared beam flares outwardly in the form of, for example, a cone of infrared light. Accordingly, in order for one of the beam receivers to be optically aligned with the mating beam projector, the use is required of a light shielding plate or the like to shield the infrared beam projected from such mating beam projector from falling onto the other of the beam receivers.
In order to alleviate the foregoing problems and inconveniences, the Japanese Laid-open Patent Publication No. 8-124042, for example, discloses an optical axis adjusting method, in which one of the beam receivers that is to be optically aligned with the beam projector then projecting an infrared beam is activated to determine the level of the infrared beam projected from the beam projector and received by such one of the beam receivers so that the optical axis alignment between each of the beam projectors and the mating beam receiver can be accomplished. In this publication, the beam receivers are provided with respective electric switches each operable to selectively switch the corresponding beam receiver on and off one at a time. According to this known method, one of the beam receivers, which is to be inputted to a signal processing circuit unit, is switched on while the other beam receiver or receivers are switched off, so that only the beam receiver to be optically aligned with the mating beam projector can be activated.
Even in the system disclosed in the second mentioned patent publication, the optical axis adjustment similarly tends to become complicated, cumbersome and time-consuming by the following reason. Specifically, since one of the beam receivers that has been switched on receives the infrared beams from both of the beam projectors, the optical axis adjustment of one of the upper and lower beam receivers requires only one of the beam projectors, which is associated with such one of the upper and lower beam receivers, to project the infrared beam. Accordingly, determination of the level of light received by each of the upper and lower beam receivers tends to be complicated and cumbersome, resulting in a substantial length of time required to accomplish the adjustment of the individual optical axes between the beam projectors and the associated beam receivers.
Also, since respective electric switches of the beam projectors and receivers are required to be operated simultaneously, a mechanism for achieving the simultaneous operation of those switches tends to become complicated and, hence, an attendant worker has to be assigned for each of the beam projector side and the beam receiver side. In addition, it often occurs that even though switch settings for the upper and lower beam receivers are in error, the optical axis adjustment tends to be performed without the erroneous switch setting being recognized.